The Shadow international development secretary mistakenly referred to Ed Milliband’s elder brother as the man she wanted to lead the party at the next election.

Speaking ahead of a speech to the Labour party conference in Liverpool, Miss Harman told the Woman’s Hour on BBC Radio 4: "I hope we will have David, er, Ed, Ed Miliband elected as Prime Minister at the next election.”

Her slip was immediately seized on by critics and users on Twitter, the microblogging site.

Last week, Ed Miliband defended the decision by his younger brother to snub this year's Labour Party conference.

Hundreds of party delegates are gathering in Liverpool, a year after Mr Miliband beat his elder brother to the party's leadership.

At a fringe event on Sunday night David Miliband dismissed reports of a rift with his brother as "hooey and nonsense" as he paid a fleeting visit to the Labour conference.

Addressing a fringe meeting exactly a year after losing the party leadership to his younger brother, the former foreign secretary insisted that he wants to see Ed in 10 Downing Street and Labour back in power.

Last year Miss Harman and David Miliband were involved in one of the more memorable moments of last year’s Labour conference.

In an attempt to please Labour’s faithful at the party’s conference in Manchester, the new leader said Labour had been “wrong” to invade Iraq.

As party delegates and supporters cheered and clapped, David Miliband – beaten by his brother in the leadership contest by a wafer thin margin – looked on stony-faced.

Alongside him Miss Harman, the deputy leader, clapped enthusiastically. Mr Miliband was caught by television cameras looking at her disdainfully before asking her: “Why are you clapping? You voted for it.”

Miss Harman appeared to reply: “I am clapping because as you know, I am supporting him.”

In her speech to delegates on Monday, Miss Harman called for a tougher tax regime for international traders and warned global companies they had responsibility not to "rip off" developing countries.

She also demanded that the world's poor were not left to "pay the price" of an economic crisis caused by the "greed" of the bankers.

Admitting it was harder to make the case for international aid out on the doorstep in a climate of tough domestic cuts, she argued Britain was still "responsible for doing what we can to save lives".

Conceding that International Development Secretary Andrew Mitchell was "fighting" to protect the plans for aid levels to reach 0.7 per cent of gross national income by 2013, she claimed "most Tories are against it".

Delegates were also told the coalition's "men-only" ministerial team, "will never be able to lead the way internationally in empowering woman and girls in the developing world".